(1) Field of the Invention
The present invention relates to an image forming apparatus and a cleaning control method, and specifically to an image forming apparatus by electrophotography provided with a charging device for charging the surface of a photoreceptor to perform image formation based on an electrostatic latent image formed on the photoreceptor, and a cleaning control method.
(2) Description of the Prior Art
An image forming apparatus by electrophotography is equipped with a charging device for uniformly charging the surface of a photoreceptor. The charging device includes, for example, a noncontact type charging device that does not come into contact with the surface of the photoreceptor. The noncontact type charging device charges the surface of the photoreceptor by discharge from an electrode to which high-voltage power supply is applied, so-called corona discharge. The noncontact type charging device includes a saw-tooth type charging device having a plurality of needle electrodes.
There is a problem for the saw-tooth type charging device that a toner, silica and dust floating in an image forming apparatus provided with the charging device are adsorbed to tip portions of saw teeth in which a high-voltage electric field is generated. Additionally, leaving such a problem prevents from performing proper discharge, and a so-called discharge defect is caused. Such a discharge defect prevents the photoreceptor from being uniformly charged, thus causing an image defect, which poses a problem.
Further, corona products such as ozone and nitrogen oxide are generated with discharge by the charging device.
There is a problem that since such nitrogen oxide, ozone, and others oxidize the surface of the photoreceptor and lower electric resistance, thereby causing electrification charge on the surface of the photoreceptor to be easily leaked, defects such as image blurring, image deletion, and white spots are caused in an image formed on the photoreceptor.
Consequently, in order to solve a conventional problem described above, a related art has been proposed that tips of saw teeth are regularly cleaned with a cleaning roller, thereby removing a toner, silica, dust and the like attached to tip portions of the saw teeth (see Patent Literature 1).
Additionally, a device has been proposed for controlling so as to operate a cleaning member when a discharge member becomes dirty in consideration of a life of a cleaning member such as a cleaning roller constituting the above-described related art (see Patent Literature 2).
Note that, in an ozone generating mechanism, ozone is generated by collision of an electron and an oxygen molecule, and thus unavoidably generated in discharge in air. The quantity of electrons generated in such discharge is increased as the amount of the current which is added to saw teeth is increased. Therefore, prevention of excessive generation thereof is allowed by decreasing the amount of the saw-tooth current.